Molding compositions from naturally occurring cellulosic materials and method for preparing the same



Patented June 16, 1942 MOLDING COMPOSITIONS FROM NATURAL- LY OCCUBRING CELLULOSIC MATERIALS AND METHOD FOR PREPARING THE SAME Ralph Oliver Phillips, Itidgewood, N. 1., and Ernst Hugo Werner Rottsieper, Epsom, England, assignors to The Forestal Land, Timber and Railways Company Limited, Epsom, England, a.

British company No Drawing. Application March 8, 1941, Serial In Great Britain February 13,

Claims. (Cl. 260-10) This invention relates to the manufacture of molded products of the phenol formaldehyde type and in particular to molding materials of the kind which include as a phenolic component a natural tanning agent.

Hitherto the tanning material employed has been extracted from the fibrous material in which it naturally occurs prior to being mixed with the other molding materials and wood fiour or similar filling materials have therefore been added to impart the necessary strength to'the molded product. The two main tanning extracts, namely quebracho and mimosa, are generally obtained in solid form containing about 80% of dry mat ter, and to improve the strength of the molded products, proposals have previously been made to impregnate the wood fiour used as a filling with a liquid tanning extract or with a solution of tanning extract obtained by dissolving the solid extract and reevaporating the solvent prior to the addition of the condensation component, i. e. the aldehyde. The present invention is based upon the discovery that by using fibrous materials which are naturally specially rich in certain tannins it is possible to produce a molded material simply by mixing the fibrous material with the aldehyde component, e. g. a formaldehyde yielding body.

According to the present invention a moldable material, e. g. a powder or sheet for use in the manufacture of molded products, comprises wood, bark or like natural tannin-containing material as hereinafter defined and an aldehyde, e. g. a

. rials which in their natural state contain tannins of the catechol type which on reacting with an aldehyde form water-insoluble condensation products. These materials are illustrative of a preferred embodiment of the invention in view .of their natural content of catechol tannins and which substantially do not hydrolyze with acids and which on reacting with an aldehyde form water-insoluble condensation. products as distinct from the pyrogallol tannins which are hydrolyzable with acids and do not yield insoluble condensation products with aldehydes. It is, of course, common practice in the plastic industries to use wood fiour as a filling material but it is well known that woods ordinarily used in the manufacture of wood flour are the soft woods, principally pine, spruce and fir which do not contain any tannin (Carleton Ellis, The Chemistry of Synthetic Resins, 1935 Edition, vol. 11, page 1273). It has been proposed hitherto to make boards by treating wood fibre which may be obtained by grinding wood to a fine powder, with a substance capable of reacting with a phenol, such as an aldehyde, to form a condensation product, and submitting the material to heat and pressure. There is no suggestion, however, that the woods to be employed should be tannin-containing woo'dsstill less is there any suggestion that woods containing catechol tannins should be em- 'ployed.

The wood or bark or like natural tannin-containing material is disintegrated as by grinding or milling prior to its admixture with the aldehyde, and the molded articles which are produced show great mechanical strength which is attribdistribution of tannin in the fibres.

uted to the relatively large amount of fibrous material employed and to the thorough natural The term powder" is to be read as including material in the form of granules or pellets in addition to the fine dust or powder referred to in the specific examples hereafter given.

It will thus be seen that according to the present invention many of the steps previously necessary in the manufacture of a molding powder or composition containing natural tanning agents are omitted and that it is only necessary to disintegrate the bark or other tannin-containing material to the requisite degree of fineness and then to mix the powder so obtained with the other molding ingredients.

' It will thus be seen that according to the present invention many of the steps previously necessary in the manufacture of a molding powder or composition containing natural tanning agents.

are omitted and that it is only necessary to disintegrate the bark or other tannin-containing material to the requisite degree of fineness and then to mix the powder so obtained with the other molding ingredients.

Preferably the aldehyde is added to the powdered tannin-containing bark or the like in solid form, e. g. paraformaldehyde, but aqueous solutions or non-aqueous solutions may also be employed.

The percentage of aldehyde necessary depends upon the quantity of taming matter which the 'terial is dried until it contains no moisture.

original materialcontains and inthe case of quebrachowooinot less thani'2% or 2/2% of..

paraformaldehyde is found suflicient to give good results, for mimosa bark a minimum of 3% to 4% is necessary and with spruce bark 2% or less is required. These percentages may be increased to suit the desired finish or degree of hardness.

A plasticiser may be added to the moldable material in particular. glycerine orother plasticisers which are soluble in water and able to dissolve the tannin in the powdered material may be added with good. results. Water or a solvent for the tanninis preferably employed to assist the flow of the powder in the mold especially if no plasticiser is employed. Colouring matter can of course be included.

In the preparation of the powder the raw material, that is to say the wood, bark, roots or other tannin-containing material, may first be dried so as to reduce its moisture content to 5% or and is then disintegrated by grinding or milling in a suitable mill to the requisite degree of fineness for example not less than that usual in the manufacture of wood filler or fiour employed in the production of plastic articles. Preliminary drying is not always essential, as good results can be obtained even if this step is omitted. By drying, however, the time occupied in grinding is reduced and in some cases the raw ma- In certain cases the-tannin content of the powdered material so obtained can be increased by the addition of tanning extract. Where, as in exceptional cases, the initial tannin content of the tanning material is high, some of the tannin may first be extracted and used for other purposes or a suitable fibrous filler may be added to compensate for any deficiency of fibre in the natural material. Thus mangrove bark may contain up to 50% of tannin and this renders advisable the addition of wood flour. The powder so produced with or without the addition of tanning extract in powdered or liquid form, is thoroughly mixed with a condensing agent such as an aldehyde and preferably a solid material such as paraformaldehyde or a polyoxymethylene is used. It is also possible to employ hexamethylene etramine.

The tannin-containing materials which can be employed includequebracho wood, mimosa bark,

which contain tannins of the condensable type.

The so-called .pyrogallol-containing materials such as valonia cups or beards, myrabolam nuts, or ground chestnut wood may be incorporated in the molding powders in small proportions but as they do not generally condense with aldehydes in the same manner as the tannin-containing materials already specified, they tend to produce a finished article which is less resistant to water and lacking the same degree of mechanical strength.

The articles produced from molding powders or material made in accordance with the present invention are strong, 0! good colour, unaffected by water and relatively elastic so that they do not readily break. In all these directions they compare favourably with articles molded from ordinary wood flour impregnated with liquid or redissolved solid tanning extracts and involve the use or smaller quantities 0! tan- 1 require the use of approximately equal quantities or tanning extract and wood flour if the:

' natural distribution of tannin in the fibrous material used, practical difilculties in the molding nin, since powders made from tanning extract operation and inconsistent results are obviated. The following specific examples are given by .way of illustration although it will be understood that the examples.

invention is not limited to these Example I 100 parts of fresh mimosa bark having a water content of 15% after preliminary drying were ground in a rod mill to a powder capable of passing through an I. M. M. mesh sieve. The powder was thoroughly mixed with 3.5 parts of paraformaldehyde and 6 parts of glycerine and subjected to thorough homogenisation. The powder so obtained when molded to form an ashtray at a temperature of 325 F. for 3 minutes at a pressure of 2 tons per square inch showed great hardness, did not crack when permitted to fall from a height of 12 feet on to a concrete floor, possessed good water. resistance and when boiled for 1 hour in water did not give up any colouring matter.

Example II 75 parts of dried larch bark and 75 parts of dried mimosa bark were ground to a, powder as already described, mixed together and incorporated with 3.3 parts of hexamethylene tetramine, 12 parts of glycerine and 20 parts 0! water. This composition yielded good products when molded under a pressure of 2 tons per square inch at temperatures from 300 to 315 F. The invention is equally applicable to the manufacture of molding materials in sheet or laminated form and it will be understood that these can be made and subsequently treated in the known manner but will include as a phenolic component naturally grown materials such as bark or wood already containing tannin and ground or otherwise treated for addition to or incorporation in the sheet or other vehicle.

What we claim as our invention and desire to secure by Letters Patent is: 4

1. A composition for making molded products comprising a disintegrated naturally occurring fibrous cellulosic material inherently containing a substantial content of catechol tannins, said material being admixed with a formaldehydeyielding body as a condensing agent. 2. A composition for making molded products comprising powdered naturally occurring fibrous tannins,saidmaterial being admixed with a form-- aldehyde-yielding body as a condensing agent, and a water-soluble plasticizer.

3. A composition for making molded products comprising naturally occurring powderedcelluloslc material inherently containing catechol tannins, said material being admixed with a formaldehyde-yielding body as a condensing agent, and with a water-soluble plasticizing material, a filler substance, and a pigment.

4. The composition as in claim 2, wherein the cellulosic material contains mimosa bark, the condensing component is paraformaldehyde, and the plasticizer is glycerine.

5. The composition as in claim 2, where the cellulosic material is dried quebracho wood, the condensing component is paraformaldehyde, and the plasticizer is glycerine and methyl lactate.

6. The composition as in claim 3, where the bark is mangrove bark, and where the filler is wood flour.

'7. The method of making a moldable material which comprises reducing a naturally occurring fibrous cellulosic material inherently containing a substantial content of catechol tannins to adisintegrated state, and admixing therewith a formaldehyde-yieldingbody as a condensing component. i

8. The method of making a moldable material which comprises reducing a naturally occurring fibrous cellulosic material inherently containing a substantial content of catechol tannins to a powdered state, adding a formaldehydeyielding body thereto as a cmidensing component, and admixing with the substances a watersoluble plasticizer.

9. The method of making a moldable material which comprises reducing a naturally occurring fibrous cellulosic material inherently containing a substantial content of catechol tannins to a disintegrated state, adding paraformaldehyde thereto as a condensing component, and admixing with these substances glycerine as a plasticizer.

10. The method as in claim '7, wherein the formaldehyde-yielding body is hexamethylene tetramine.

RALPH OLIVER PHILLIPS. ERNST HUGO WERNER RO'I'ISIEPER. 

